The present invention relates to a bumper system for a vehicle and, more particularly, to such a bumper system in which a curved vehicle bumper member is connected directly to longitudinally extending load bearing members which are part of the vehicle. This bumper system may be utilized with motor vehicles of the type having a separate frame or with motor vehicles having unibody construction.
Bumpers are used on motor vehicles to absorb low level impact forces and to limit the amount of damage sustained to the vehicle body during high level impacts. It is desired that permanent damage caused by a crash be confined, to the degree possible, to the bumper structure itself. This facilitates repair, since only the damaged bumper must be replaced. With impacts of any level, it is desired that the energy of impact be absorbed or dissipated without permanently deforming the main structure of the vehicle, including the parallel, laterally spaced pair of load bearing members which extend longitudinally to the front and to the rear of the vehicle, and to which a vehicle bumper system may commonly secured.
A number of prior art bumper systems have included a spring support arrangement for securing a bumper to the longitudinally extending load bearing members of a vehicle. One such system is shown in U.S. Pat. No. 1,485,042, issued Feb. 26, 1924, to Lyon. The '042 Lyon patent discloses a bumper structure, including a generally straight bumper member, which attaches to the ends of the frame rails of an automobile, and which incorporates a straight member bridging the points of attachment.
U.S. Pat. No. 1,626,347, issued Apr. 26, 1927, to Lyon, discloses a curved bumper in conjunction with a member extending across the vehicle frame and having a lateral "bracing action" on the vehicle frame at the points of attachment. The '347 Lyon patent, like the '042 Lyon patent, relates to a bumper system in which the bumper is attached to the vehicle frame through an intermediate spring support structure. Depending upon the relative stiffness of the components of this bumper and further depending upon the nature of the impact force to the bumper, it is possible that the load bearing rails could be subjected, by an impact force applied to the bumper, to inward or outward lateral forces, no lateral forces, or lateral forces directed in the same direction.
With the bumper systems disclosed in the Lyon patents, a spring mounting arrangement is provided to attach the bumper to the vehicle frame. One problem with such a spring mounting arrangement is that it results in only relatively low level forces being applied to the bumper system during the initial movement of the bumper at impact. Since very little energy is absorbed during this initial displacement of the bumper, and since a fixed amount of energy must be absorbed in any given collision, a substantial amount of movement of the bumper must be permitted. It will be appreciated that this results in a vehicle which is longer than would otherwise be necessary in order to permit the rather large deflection of the bumper system.
Optimally, a bumper system should be designed so that the reaction force applied to the bumper during an impact increases quickly to a maximum level as the bumper is displaced, and then remains relatively constant when as the bumper undergoes further displacement. This results in the maximum amount of energy being absorbed for a given amount of bumper displacement, with the reaction force experienced by the bumper and load bearing members to which the bumper is attached being limited to a desired level.
It is seen, therefore, that there is a need for a bumper system in which the reaction force level experienced at impact by a bumper system increases rapidly to a predetermined level and thereafter remains generally constant, and in which the likelihood of damage to the vehicle is reduced.